Ship&#39;s propulsion plant

ABSTRACT

A device for automatically isolating a ship&#39;&#39;s propulsion plant from the propeller in emergency situations. When the tractive torque of the propeller acting opposite to the direction of rotation of the engine exceeds a predetermined limiting value, a selectively engageable mechanical coupling which by-passes the hydrodynamic coupling is positively disconnected through the action of a safety coupling element. A coarse-pitch screw coupling forces an axially movable gearshift sleeve into the engaged position via a spur-tooth gear coupling when transmitting forward engine rotation, and alternatively moves the sleeve to disengage the spur-toothed coupling when reverse torque exceeds the limiting value.

Jahnel et al.

1 1 SHIPS PROPULSION PLANT [75] Inventors: Ernst Jahnel, Augsburg; Erich John,

Gersthofen, both of Germany; Harold Sinclair, Folkestone, England [73] Assignee: Messrs. Zahnraderfabrik Renk Aktiengesellschaft, Augsburg DT [22] Filed: Sept. 25, 1973 [21] Appl. No.: 400,661

[30] Foreign Application Priority Data Sept. 29, 1972 Germany 2247964 [52] US. Cl. 192/328; 115/34 R [51] Int. Cl. F16d 39/00; Fl6d 9/00 [58] Field of Search 192/328, 3.29, 3.3, 57, 192/94; 115/34 R [56] References Cited UNITED STATES PATENTS 1,986,442 1/1935 Koursh 1 192/94 2,093,498 9/1937 Walti 192/329 2,613,503 10/1952 Syrovy..... 192/3 3 2,616,311 11/1952 Lapsley 192/3 3 2,652,730 9/1953 Newcomb .1 192/33 oooooooo Primary Examiner-Trygve M. Blix Assistant ExaminerGalen L. Barefoot Attorney, Agent, or Firm-Weingarten, Maxham & Schurgin [57] ABSTRACT A device for automatically isolating a ships propulsion plant from the propeller in emergency situations. When the tractive torque of the propeller acting oppo site to the direction of rotation of the engine exceeds a predetermined limiting value, a selectively engageable mechanical coupling which by-passes the hydrodynamic coupling is positively disconnected through the action of a safety coupling element. A coarse-pitch screw coupling forces an axially movable gearshift sleeve into the engaged position via a spur-tooth gear coupling when transmitting forward engine rotation, and alternatively moves the sleeve to disengage the spur-toothed coupling when reverse torque exceeds the limiting value.

18 Claims, 6 Drawing Figures 'PMENTEUJUH 31975 3.8871148 SHEET 3 3 15 8b 16 A 17 g- PATENTEB m 3 I975 FIG. 4

SHEET O O O FIG. 6

SHEET PATENTEBJ N3 1915 O @OGQQG E 2 m9 m2 SHIPS PROPULSION PLANT FIELD OF THE INVENTION The invention relates to a ships propulsion plant having at least one diesel engine, a variable-filling hydrodynamic coupling connected between the engine and the propeller and a shiftable mechanical coupling to bypass the hydrodynamic coupling, and more particularly concerns a means for isolating the engine from the propeller in emergency situations.

DISCUSSION OF THE PRIOR ART Such types of ships propulsion plants are already known in numerous embodiments. For example, one embodiment of such a ships propulsion plant is described in German patent publication (Offenlegungss chrift) No. 1,781,141 corresponding to US. Pat. No. 3,539,045.

In conjunction with diesel drives in shipbuilding there is a more and more frequent requirement that it be possible to isolate the engine from the ships propeller instantaneously in the event that engine damage occurs, This requirement arises because, particularly with the medium-speed highly-charged diesel engines now frequently used, in the event of the occurrence of engine damage the continued running of the engine under the action of the tractive torque of the ships propeller can lead very rapidly to devastating destruction to the engine and to the gear unit.

In recent times, shiftable gear couplings are being used to an increasing degree as by-pass couplings for hydrodynamic couplings. As is known, due to the tooth-flank friction, gear couplings can be shifted only with little or no torque loading. Consequently, when using a shiftable gear coupling to by-pass the hydrodynamic coupling in ships propulsion plants of the initially described general construction, it can happen that, after emitting a signal announcing an engine damage, the tractive torque of the ships propeller which becomes active immediately after occurrence of the engine damage and which bears on the tooth flanks of the by-pass coupling makes impossible an instantaneous disengagement of the by-pass coupling. Thus the mentioned destruction occurs quickly before the tractive torque has dropped to a lower value permitting disengagement of the coupling.

SUMMARY OF THE INVENTION The task to be solved by the invention is to bring about an automatic isolation of the propulsion engine from the ships propeller in ships propulsion plants of the intially described construction in the event that upon sudden sharp drop of rotational speed or standstill of the propulsion engine the tractive torque of the ships propeller exceeds a certain value generally corresponding to the no-load braking torque of the propulsion engine. No-load braking torque may be defined as that torque which may be normally utilized during speed reduction to decelerate the ship by means of the dragged propeller.

This task is solved according to the invention in that the bypass coupling interacts with a preor postconnected one-way safety coupling element which is so designed that when the bypass coupling is engaged and the torque is transmitted in the direction of rotation of the diesel engine drive, it causes no influence on the bypass coupling. When the torque is transmitted opposite to the direction of rotation of the diesel engine drive, it releases the bypass coupling by generating a disconnecting force on it after exceeding a limiting torque in the range of the no-load braking torque of the diesel engine.

The invention is applicable preferably to ships propulsion plants in which a gear coupling is used as the by-pass coupling for the hydrodynamic coupling. However, it is also applicable to ships propulsion plants in which other types of couplings are used as the by-pass coupling for the hydrodynamic coupling.

In comparison with known ships propulsion plants of the initially described general type of construction, the invention offers the technical advance that if, upon occurrence of engine damage, for any reasons an immediate disengagement of the coupling by-passing the hydrodynamic coupling is not possible, this coupling becomes inactive automatically as soon as the tractive torque of the ships propeller overrunning the propulsion engine exceeds the mentioned limiting value. Since the hydrodynamic coupling is always drained when the by-pass coupling is engaged, when the by-pass coupling becomes inactive there immediately occurs a complete isolation of the propulsion engine from the ships propeller so that the damaged propulsion engine slows down only under its self-torque and quickly comes to a halt and thus greater and more serious damage can be avoided. The circumstance that torques exceeding the mentioned limiting value are unable to be transmitted when the by-pass coupling is engaged and the propulsion engine is rotating backwards in the arrangement according to the invention represents no drawback provided that long periods of backward travel with engaged by-pass coupling do not occur in practice and only the hydrodynamic coupling is used during maneuvering movements. Damage of the mentioned type can hardly be anticipated here due to the partial loading of the engine.

According to a preferred embodiment of the ships propulsion plant of this invention, a mechanically, pneumatically or hydraulically shiftable gear coupling is used to by-pass the hydrodynamic coupling. This embodiment of the invention is characterized in that the gearshift sleeve of the gear coupling can be coupled to one coupling half of the hydrodynamic coupling via a coarse-pitch screw coupling and can be coupled to the other half of the hydrodynamic coupling via a spurtoothed gear coupling system. The coarse-pitch screw coupling forming one part of the one-way safety coupling element forces the gearshift sleeve into the engaged position when transmitting the propulsive torque in the forward direction of rotation. In the shift-force transmission path between the control device and the gearshift sleeve there is arranged a spring link forming another part of the one-way safety coupling element or a pressure limiting valve, which, when the control device is set to engagement of the by-pass coupling, permits the gearshift sleeve to be displaced axially in the direction of disengagement of the by-pass coupling upon exceedance of the limiting torque under the action of the coarse-pitch screw coupling against the ac tion of the spring link or of the shift fluid pressure determined by the setting of the pressure limiting valve.

This embodiment of the invention offers the advantage that the torque limiter can be arranged not in the bypass coupling itself but rather in the mechanical or hydraulic shift-force transmission path between the control device and the by-pass coupling, so that no design complication results in regard to the hy-pass coupling itself. Since the transmission of shift force from the control device to the gearshift sleeve of the by-pass coupling is usually effected mechanically or hydraulically anyway, the torque limiter can thus have the form of a simple spring or a simple pressure limiting valve due to the conversion according to the invention, of the propellers tractive torque into an axial force urging the gearshift sleeve into the disengaged position.

This method of construction makes it possible to accommodate the by-pass coupling in a known manner inside the housing of the hydrodynamic coupling.

According to a second preferred embodiment of this invention a hydraulically shiftable gear coupling is provided as a by-pass for the hydrodynamic coupling. The gearshift sleeve of the gear coupling is built as a movable cylinder of a double-acting cylinder-piston arrangement whose piston is rigidly connected to the cylinder and whose piston encloses an extension of the drive shaft which is provided with inlet and outlet channels projecting into the cylinder volumes for the pressure fluid controlled by the control device.

As a modification of this, in a kinematic reversal of such an arrangement the gearshift sleeve can also be built as a piston of a double-acting cylinder-piston arrangement whose cylinder is formed on an associated coupling shaft which is provided with inlet and outlet channels projecting into the cylinder volumes for the pressure fluid controlled by the control device.

Such arrangements result in a particularly compact, spacesaving and light-weight construction.

According to a further development of the second preferred embodiment of this invention, into the two cylinder volumes of the cylinder-piston arrangement formed between the gearshift sleeve of the by-pass gear coupling and the associated coupling shaft there project radial branch channels that are connected to an alarm line leading to an indicating mechanism, signalling mechanism or servomechanism. The gearshift sleeve is provided with axial grooves or circular grooves which are distributed along the periphery and which are axially dimensioned and arranged in such a manner that the branch channel associated with the engaged position of the gearshift sleeve of the by-pass coupling is connected to the alarm line only in the engaged final position of the gearshift sleeve and further in such a manner that the branch channel associated with the disengaged position of the gearshift sleeve is connected to the alarm line at least in the engaged final position of the gearshift sleeve.

Such an arrangement makes it possible to provide the engine personnel with a continuous indication that the by-pass coupling is in the fully engaged or fully disengaged final position and to also provide a signal via a servomechanism, possibly connected to the alarm line, when the gearshift sleeve is about to move out of the fully engaged or fully disengaged final position into the other or opposite position.

In still another form of the just described embodiment of the invention, in the pressure fluid line associated with the engaged position of the gearshift sleeve of the by-pass coupling there can be arranged a pressure-release valve which is actuated by a servomechanism connected to the alarm line and which opens when the pressure drops in the alarm line.

By means of this arrangement it is ensured that when the gearshift sleeve of the bypass coupling is displaced out of the engaged final position because of an exceedance of the limiting value of tractive torque, the fluid pressure holding the gear-shift sleeve in the engaged position is released instantaneously so that the gearshift sleeve can be displaced very quickly into the disengaged position.

In a further development of the invention, the pressure release valve arranged in the mentioned pressure line can also be openable by hand, preferably from the control device, and/or via a servomechanism by means of a signal from a temperature monitor arranged on the propulsion engine.

By means of such an arrangement it is possible for the engine personnel to initiate the disengagement of the by-pass coupling immediately after visual discovery of engine damage, without first having to wait for its automatic disengagement due to exceedance of the limiting value of tractive torque. The actuation of the pressure release valve by the signal from a temperature monitor arranged on the propulsion engine makes it possible to initiate the automatic disengagement of the by-pass coupling upon occurrence of an abnormal operating condition in the propulsion engine.

The leading faces of at least one gear ring of the spurtoothed gear coupling system of the by-pass gear cou pling can be provided in a known manner with deflection bevels which prevent an engagement of the by-pass coupling as long as the hydrodynamic coupling half associated with the ships propeller overruns the hydrodynamic coupling half associated with the diesel engine.

This beveling of the leading edges provides the long known and frequently applied synchronization benefits, but has the disadvantage that in the event of hydraulic shifting of the gearshift sleeve of the bypass gear coupling in the pressure fluid lines when there is an overrunning of the hydrodynamic coupling half associated with the propeller shaft, rhythmic pressure surges or oscillations occur in the pressure fluid lines which depend on the coupling tooth pitch and on the rotation speed difference. Such oscillations are more harmful the larger the ratio of the amount of pressure fluid situated in the cylinder volumes of the cylinderpiston arrangement effecting the shifting of the gearshift sleeve of the bypass gear coupling to the crosssection and to the length of the pressure lines leading to the control device.

Consequently, as a further development of the invention, to the cylinder volume of the mentioned cylinderpiston arrangement associated with the engagement of the by-pass coupling there are connected one or more elastic reservoirs which are capable of holding that amount of fluid that is displaced by the axial back-andforth motion of the gearshift sleeve during the scraping over each other of the bevelled leading faces of the spur-toothed gear coupling system of the gearshift sleeve or of its counter gear-tooth system prior to its engagement by the piston.

The elastic reservoir or reservoirs preferably have the form of boreholes which on one hand empty into the relevant cylinder volume of the cylinder-piston arrangement and on the other hand are connected to a nonpressurized volume of the coupling arrangement and in which boreholes spring-loaded small pistons can be displaced within limits.

BRIEF DESCRIPTION OF THE DRAWING The objects, advantages and features of this invention will become more apparent from the following detailed description of two embodiments of the invention, taken in conjunction with the drawing in which:

FIG. 1 is a schematic partial axial section through a hydrodynamic coupling together with an associated bypass gear coupling of one embodiment of a ship's propulsion plant constructed according to the invention;

FIG. 2 is a schematic axial section through a hydrodynamic coupling together with associated by-pass gear coupling of another embodiment of a ships propulsion plant constructed according to the invention;

FIG. 3 depicts a cutaway portion of the-axial section shown in FIG. 2 on a larger scale, the top half of the figure showing the gearshift sleeve in the engaged position, the bottom half being in the disengaged position;

FIG. 4 is a schematic diagram of a ships propulsion plant according to the invention with mechanical shifting of the by-pass coupling;

FIG. 5 is a schematic diagram of a ships propulsion plant according to the invention with hydraulic shifting of the by-pass coupling, and

FIG. 6 is a development diagram of the spur-toothed gear rims of the by-pass coupling.

The drive shaft 1 of the coupling arrangement illustrated in FIG. 1 is connected via a rotary-flexible coupling 101 illustrated in FIG. 4 to the crankshaft ofa diesel engine 102 likewise illustrated in FIG. 4. Fastened to the drive shaft 1 are a twin pump impeller 2 of a hydrodynamic coupling and a shaft connecting piece 4 provided with a coarse-pitch external thread. Fastened to the housing 5 of the hydrodynamic coupling are the two turbine wheels 6 of the hydrodynamic coupling and a hollow shaft 7, which latter is rigidly coupled to the driven shaft 8 to which in turn is fastened the pinion 103 of a ships gear unit via which the propeller shaft 104 is driven. The drive shaft 1 is supported on one hand in a main bearing 9 and on the other hand in a hollow-shaft connecting piece 10 fastened to the driven shaft 8. To one of the turbine wheels 6 of the hydrodynamic coupling is fastened a hollow-shaft connecting piece 11 which is supported in a main bearing 12 into whose bearing block empties an inlet channel for the operating fluid of the hydrodynamic coupling, which fluid goes from there in the usual manner into the working chambers of the hydrodynamic coupling via a circular channel and axial channels. The means for altering the filling ofthe hydrodynamic coupling are indicated at 105 in FIG. 4, but do not belong to the invention. The driven shaft 8 is supported in a main bearing 13.

The hollow shaft 7 has a spur-toothed internal gear ring 14. Axially displaceable inside the hollow shaft 7 is a gearshift sleeve 15 which on one hand is permanently engaged with the coarse-pitch external thread 3 of the drive shaft 1 by means of a coarse-pitch internal thread 16 and on the other hand has a spur-toothed external gear ring 17 which is engageable by axial displacement of the gearshift sleeve 15 in the internal gear ring 14 of the hollow shaft 7. In a shift groove 18 of the gearshift sleeve 15 there engages a shift bolt 20 of an axially displaceable shift bush 21 which embraces the hollow shaft 7 and its longitudinal slit 19. The bolt 20 projects through the longitudinal slit 19 of the hollow shaft 7. In the shift groove 22 of the shift bush 21 there engages a shift fork 23 which is axially displaceable by means of an angle lever 24 and a shift linkage 25 leading to a nonillustrated control device. The shift sleeve 15 guided at one of its ends through the coarse-pitch screw coupling 3, 16 is supported in the disengaged condition illustrated in FIG. 1 by means of an internal collar on a corresponding external collar of the drive shaft 1. This sleeve can be supported during its axial displacement in the engagement direction by means of an internal lip at its other end on a slide ring fastened to an external collar of the hollow-shaft connecting piece 10, and in the engaged condition, it is guided by the reciprocal engagement of the spur-toothed gear rings 14, 17. If the shift sleeve 15 is situated in the engaged position, then it connects the drive shaft 1 directly to the hollow shaft 7 via the permanently engaged coarse-pitch screw coupling 3, 16 on the one hand and via the mutually engaged spur-toothed gear rings 14, 17 on the other hand and thus connecting the drive shaft directly to the driven shaft 8, so that the hydrodynamic coupling 2, 5, 6 is by-passed.

In the usual manner, the control device indicated in FIG. 4 has members 106, 107 and 108 for setting the power of the diesel engine, setting the filling of the hydrodynamic coupling 2, 5, 6 and shifting the by-pass coupling 3, 16, 15, 17, 14 respectively. Indicated at 109 is an optional reversing device for the diesel engine 102. The transmission of shift force from the control device to the shift linkage 25 can be effected either mechanically or hydraulically. If the transmission of shift force is effected mechanically, then between the control device 108 and the shift linkage 25 there is connected a laminated spring 110 shown in FIG. 4 which endeavors to force the gearshift sleeve 15 of the bypass coupling 3, 16, 15, 17, 14 into the engaged position. The spring excursion of the laminated spring and the shift excursion of the shift linkage are so adapted to one another that when the gearshift sleeve 15 is engaged and when the control device 108 is set to by-pass the hydrodynamic coupling 2, 5, 6, the spring excursion of the laminated spring must be overcome when the gearshift sleeve 15 is displaced forcefully from the engaged position into the disengaged position in opposition to the setting of the control device.

The thread direction of the coarse-pitch thread 3, 16 is so chosen that when the diesel engine rotates in the forward direction the drive shaft 1 endeavors to force the shift sleeve 15 into the engaged position via the coarse-pitch thread 3, 16. If the control device is situated in the setting shown in FIG. 4 in which the gearshift sleeve 15 is situated in the disengaged position shown in FIG. 1 and the hydrodynamic coupling 2, 5, 6 is filled, then the laminated spring 110 situated in the shift force transmission path of the shift linkage 25 is inactive, that is, the shift linkage 25 acts as a rigid linkage and the propulsive torque of the diesel engine cannot force the gearshift sleeve 15 into the engaged position via the coarse-pitch thread 3, 16, so that the force is transmitted exclusively via the hydrodynamic coupling 2, 5, 6. This applies for maneuvering speed.

If the control device is set to cruising speed, then the shift linkage 25 moves the gearshift sleeve 15 into the engaged position as long as the fluid-flow coupling 2, 5. 6 is still filled, so that the synchronization effect of the hydrodynamic coupling is still exploited in regard to the engagement of the spur-toothed gear rings l4, 17, provided that the ship is in the upper speed range and the idling diesel engine 102 is dragged by the ships propeller. Then the hydrodynamic coupling is drained and the propulsive torque of the forward-rotating diesel engine keeps the gearshift sleeve in the engaged position due to the axial thrust action of the coarse-pitch thread 3, 16.

If the rotational speed of the diesel engine is lowered or if it is stopped, then, due to the tractive torque of the ships propeller transmitted via the gear unit, the driven shaft 8 has a tendency to overrun the drive shaft 1. The spring force of the laminated spring 110 connected before the shift linkage 25 is chosen so large that the axial thrust of the shift fork 23, which is due to this laminated spring and which counteracts an axial displacement of the gearshift sleeve 15 in the direction of disengagement, is so large that the gearshift sleeve 15 is able to transmit a fully determined torque at the coarsepitch thread 3, 16. The magnitude of this torque is so suitably adjusted by means of the laminated spring 110 connected before the shift linkage 25 that it is somewhat larger than the no-load braking torque of the diesel engine 102, so that, when the control device is set to cruising speed and the diesel engins rotation speed is reduced or it is stopped, the no-load braking torque of the diesel engine can be exploited to slow down the ship via the ships propeller.

lf, when the control device is set to cruising speed, that is, when the by-pass coupling 3, 16, 15, 17, 14 is engaged while the hydrodynamic coupling 2, 5, 6 is drained and the diesel engine 102 is set to full speed ahead, a sudden damage occurs to the engine which leads to an instantaneous sharp drop of rotation speed or to an instantaneous halt of the diesel engine, then, due to the tractive torque exerted by the propeller shaft 104, the driven shaft 8 also instantaneously has the tendency to overrun the drive shaft 1, whereupon the tractive torque exceeds the mentioned limiting torque value. The tractive torque acting at the coarse-pitch screw coupling 3, 16 is converted by the latter into an axial thrust of the gearshift sleeve 15 in the disengagement direction of the spur-toothed gear rings 17, 14, which in the shift linkage 25 leads to an axial thrust that is stronger than the spring force of the laminated spring 110 connected between this shift linkage and the control device 108. Since the hydrodynamic coupling 2, 5, 6 is drained, upon overcoming this spring force the gearshift sleeve 15 can move unhindered in the disengagement direction and the coupling between the drive shaft 1 and the driven shaft 8 is instantaneously interrupted so that the diesel engine 102 suffering the damage is left to itself and greater damage to the diesel engine or to the coupling arrangement or to the gear unit is consequently avoided. To the laminated spring 110 connected between the shift linkage 25 and the control device 108 there can be connected a nonillustrated mechanism which actuates the shift linkage in the direction of a disengagement of the by-pass coupling 3, l6, l5, l7, 14 so that there is avoided a scraping over each other of the gear ring faces of the by-pass coupling, on the one hand, and a reengagement of the bypass coupling as the propellers tractive moment gradually becomes smaller, on the other hand. Thus, the diesel engine 102 suffering the damage, dependinng on the particular circumstances of the damage can slow down by itself unloaded by the rotating masses of the coupling arrangement, gear unit, shafting 104 and propeller and also unloaded by the mass of the still gliding ship, although the control device is still set to cruising speed. If the control device is set to Stop. then the mechanism that holds in a deflected states the laminated spring connected between the shift linkage 25 and the control device becomes inactive and the plant is again in the normal operating state, so that normal operation of the plant can be resumed again after eliminating the engine damage.

Instead of a laminated spring between the shift linkage 25 and the control device it obviously is also possible to interpose any other type of thrust limiter. Thus, for example, by interposing a cam connection. cam disk connection or bent-lever connection, the linear spring characteristic of the laminated spring can be converted into a bent characteristic more favorable for the present instance. Between the shift linkage 25 and the control device there can be connected a hydraulic shift-force transmission in which there is a pressure limiting valve that opens as soon as the gearshift sleeve 15 experiences an axial thrust acting in the disengagement direction which corresponds to a propeller tractive torque that is greater than the set limiting torque valve.

With reference to FIGS. 2, 3 and 5, another embodiment of a ships propulsion plant according to the invention is now described, wherein parts identical with the coupling arrangement illustrated in FIG. 1 are designated with like reference numbers in each instance.

The drive shaft 1, which is coupled via a rotaryflexible coupling 101 illustrated in FIG. 5 to a diesel engine 102 also illustrated in FIG. 5 and is constructed as a hollow shaft and is supported in a main bearing 26, is connected rigidly to one pump impeller 2 of a hydrodynamic coupling whose other pump impeller 2 is connected rigidly to the first pump impeller in the usual manner through the housing 5 of the hydrodynamic coupling. To the other pump impeller 2 is fastened a hollow-shaft connecting piece 28 which is supported in a main bearing 27 and in which is supported the driven shaft 8 which penetrates through it. To a flange of the driven shaft 8 is fastened a twin turbine wheel 6 of the hydrodynamic coupling. The inlet and outlet of the operating fluid for the hydrodynamic coupling is effected in the usual manner via axial and circular channels. This inlet and outlet of the operating fluid of the hydrodynamic coupling is effected under the control of a control device 107, illustrated in FIG. 5, in a known manner and is not part of the invention. An extension 8a of the driven shaft 8 passes through the cavity of the drive shaft 1 and is supported therein by an intermediate bearing 29. To the drive shaft 1 is fastened a ring 30 with a spur-toothed internal gear ring 14 whose details are evident from FIG. 3. Likewise evident from FIG. 3 are details of a sleeve part 32 which is fastened to the twin turbine wheel 6 and thus to the driven shaft 8. The sleeve part 32 is provided with a coarse-pitch internal thread 16 in which engages the coarse-pitch external thread 3 ofa gearshift sleeve 15 which is furthermore provided with a spur-toothed external gear ring 17 which is engageable in the spur-toothed internal gear ring 14 of the ring 30.

The gearshift sleeve 15 is illustrated in the upper half of FIG. 3 in a position in which its external gear ring 17 is engaged in the internal gear ring 14 of the ring 30, while in the lower half of FIG. 3 it is illustrated in a position in which its external gear ring 17 is disengaged from the internal gear ring 14 of the ring 30.

Because of the coarse-pitch screw coupling 3, 16 which is in permanent reciprocal engagement. the gearshift sleeve l is always connected in a limited axiallyscrewing displaceable manner with the sleeve part 32 and thus with the driven shaft 8 and is connected in a rotationally fixed manner to the drive shaft I when the external gear ring 17 is engaged in the internal gear ring 14. The axial displacement excursion of the gearshift sleeve is limited on the one hand by an inner collar 32a of the sleeve part 32 interacting with the front face of the external coarse-pitch thread 3 and on the other hand by an internal collar of the gearshift sleeve I5 interacting with an external collar 8b of the extension 80 of the drive shaft 8, with the gearshift sleeve representing the piston of a cylinder-piston arrangement. The gearshift sleeve 15 is guided axially on one hand by the permanent engagement of the coarse-pitch screw coupling 3, l6 and on the other hand by the mutual application between its internal wall and the external col- Iar 8b of the extension 8a of the driven shaft 8, and further by the permanent application of the inner face of its internal collar 15a onto this extension 8a of the driven shaft, and finally in the engaged position by the reciprocal engagement of the gear rings 14 and 17.

The cylinder of the mentioned cylinder-piston arrangement is built as a double-acting cylinder and is bordered first of all by the external collar 81) of the extension 8a, further by the cylindrical face of the extension 8a of the driven shaft 8, further by the cylindrical inner face of the gearshift sleeve 15 and finally by an external collar 80 of the extension 8a of the driven shaft 8. The two cylindrical volumes of this doubleacting cylinder are designated by A and B and are separated from each other by the internal collar 15a of the gearshift sleeve 15, the internal collar being designated as the piston in accordance with the following description. The cylindrical inner face of the gearshift sleeve 15 lies closely against the cylindrical outer faces of the external collars 8b and 8c of the extension 811 of the driven shaft 8, and the cylindrical inner face of the piston 15a of the gearshift sleeve lies closely against the cylindrical outer face of the extension 80 of the driven shaft 8. A pressure fluid channel 33 which runs inside the drive shaft 8 and which is designated subsequently as the engagement channel empties into the cylindrical volume A immediately adjacent to the external collar 8b of the extension 8a of the driven shaft 8, and a pressure fluid channel 34 which likewise runs through the driven shaft 8 and which is designated subsequently as the disengagement channel empties into the cylindrical volume B immediately adjacent to the external collar 8c of the extension 8a of the driven shaft 8. Another channel 35 designated subsequently as the alarm channel likewise passes through the driven shaft 8 and branches into two branch channels 3512 and 350 which both run radially with respect to the extension 8a of the driven shaft 8 and of which one empties onto the outer face of the external collar 8b while the other branch channel 35c empties onto the outer face of the external collar 8c of the extension 8a of the driven shaft 8. As is evident from FIG. 2, the three pressure fluid lines 33, 34 and 35 are conducted radially outward at suitable points of the driven shaft 8 and via annular grooves not illustrated in the drawing are conducted over into a stationary take-off ring 36 from where they are connected via stationary lines illustrated in FIG. 5 to a control slide valve 111 arranged in the control device or to an indicating or signaling mechanism arranged suitably on the control board or to a servomechanism 112 indicated in FIG. 5. By means of the control slide valve 111 of the control device. pressure fluid supplied from a pressure fluid source 113 can be delivered optionally to the engagement channel 33 or to the disengagement channel 34 or it can be discharged from these channels. If pressure fluid arrives in the engagement channel 33 and if pressure fluid can emerge via the disengagement channel 34, then the pressure fluid delivered via the engagement channel 33 arrives into the cylindrical volume A and endeavors to move the piston 15a in the direction ofthe cylindrical volume 8, so that the gearshift sleeve 15 forming a common part with the piston 15a attempts to move out of the position illustrated in the lower half of FIG. 3, in which its spur-toothed gear ring 17 is disengaged from the spur-toothed gear ring 14 of the ring 30, and into the position illustrated in the upper half of FIG. 3. As soon as the two gear rings 14 and 17 have come into engagement, the coarse-pitch screw coupling 3, 16 causes an axial displacement of the gearshift sleeve 15 in the usual manner when the drive shaft 1 overruns in the drive rotation direction and thus causes the complete reciprocal engagement of the spur-toothed gear rings l4, 17. If the bypass gear coupling is to be disengaged, then the driving diesel engine 102 is throttled, whereupon the driven shaft 8 which is subjected to the tractive torque of the ship's propeller causes the gearshift sleeve 15 to move into the disengaged position in the usual manner via the coarse-pitch screw coupling 3, l6. Simultaneously, pressure fluid arrives into the disengagement channel 34 and fluid can emerge via the engagement channel. so that the pressure fluid enters into the cylindrical volume B and holds the piston 15a moving in the direction of the cylindrical volume A and with it the gearshift sleeve 15 in the disengaged position illustrated in the lower half of FIG. 3.

The driven shaft 8 is connected to the propeller shaft 104 via a gear unit illustrated in FIG. 5. The thread direction of the coarse-pitch screw coupling 3, 16 is so chosen that when the gear rings 14 and 17 are engaged in each other the forward-running diesel engine 102 drives the drive shaft 1 and therewith the gearshift sleeve 15 in a rotational direction in which the force of reaction of the coarse-pitch screw coupling 3, 16 endeavors to keep the gearshift sleeve 15 in the engaged state in which the gear coupling 14, 17, 15, 3, 16 bypasses the fluidflow coupling. If the rotational speed of the diesel engine is reduced, then, due to the tractive torque of the ships propeller conducted into the driven shaft 8 via the gear unit, the driven shaft 8 endeavors to overrun the drive shaft I and, via the coarse-pitch screw coupling 16, 3, to pull the gearshift sleeve 15 out of the engaged position illustrated in the upper half of FIG. 3 and into the disengaged position illustrated in the lower half of FIG. 3. Arranged in the engagement channel 33 or in the line connected to it or at a suitable point in the control device is a pressure limiting valve 114, indicated in FIG. 5, by means of which the fluid pressure prevailing in the cylindrical volume A when the gearshift sleeve I5 is engaged is limited to a definite value which corresponds to a definite axial thrust which in turn is equal to the axial component which generates a tractive torque of the ships propeller acting on the coarse pitch screw coupling 3, 16 and introduced via the driven shaft 8. This tractive torque or the fluid pressure corresponding to this tractivc torque which prevails in the cylindrical volume A when the gearshift sleeve is engaged is in turn so suitably adjusted that it is somewhat larger than the no-load braking torque of the diesel engine, so that this no-load braking torque can be exploited for braking the ship when reducing speed.

If when the control device is set to cruising speed thereby engaging gearshift sleeve 15, a damage occurs to the diesel engine which leads to a sudden very sharp drop in rotation speed or to a halting of the diesel engine 102, then the tractive torque of the propeller exceeds the no-loacl braking torque of the diesel engine. At that time the pressure prevailing in the cylindrical volume A exceeds the pressure to which the pressure limiting valve is set, and the pressure limiting valve opens, so that now, under the action of the propeller tractive torque being applied to the coarse-pitch screw coupling 16, 3, the gearshift sleeve 15 moves out of the engaged position illustrated in the upper half of FIG. 3 and into the disengaged position illustrated in the lower half of FIG. 3 while squeezing out the pressure fluid situated in the cylindrical volume A via the engagement channel 33. Thus the drive shaft is instantaneously isolated from the driven shaft 8, that is, the diesel engine 102 is isolated from the propeller shaft 104. This axial displacement of the gearshift sleeve is effected easily because the hydrodynamic coupling 2, 5, 6 is drained when the control device 106 is set to cruising speed, that being when the control slide valve 111 is set to the engagement position of the gearshift sleeve 15.

At the cylindrical inner face of the gearshift sleeve 15, a number of axial grooves 37 are distributed along the periphery in the cylindrical volume A and are so applied and are of such a longitudinal dimension that when the gearshift sleeve 15 is in the engaged position they just connect the cylindrical volume A to the branch channel 35b and thereby to the alarm channel 35. If the gearshift sleeve 15 moves out of the engaged position into the disengaged position, then the axial grooves 37 are immediately covered by the cylindrical outer face of the external collar 8b of the extension 8a of the driven shaft 3 and then the mouth of the branch channel 35b at the cylindrical outer face of this external collar 8b is covered by the cylindrical inner face of the gearshift sleeve 15 so that there is no longer any connection between the cylindrical volume A and the alarm channel 35. Moreover, on the cylindrical inner face of the gearshift sleeve 15 there is an annular groove 38 which is so arranged and whose width is of such a dimension that, as is evident from the lower half of FIG. 3, when the gearshift sleeve 15 is in the disengaged position it connects the branch channel 35c of the external collar 80 of the extensionn 8a of the driven shaft 8 and thus also the alarm channel 35 to the cylindrical volume B. As is evident from the ripper half of FlG. 3, when the gearshift sleeve is in the engaged position, groove 38 lies completely outside the cylindrical volume 8 on the other side of the external collar 80 so that the mouth of the branch channel 35!) in the cylindrical outer face of the external collar 8c is covered by the cylindrical inner face of the gearshift sleeve 15 remaining next to the annular groove. Thui when the gearshift sleeve 15 is in the disengaged position and during a large part of the displacement path-, of the gearshift sleeve 15 out of the disengaged position into the engaged position, the cylindrical volumt- B is connected to the alarm channel 35 and this connection is interrupted only just before the gearshift sleeve 15 has reached its engaged final position. Due to this special construction and width of the annular groove 38, the external collar 8(- of the extension 8a of the driven shaft 8 acts together with the cylindrical inner face of the gearshift sleeve 15 in a known manner as a damper which damps rapid axial movements of the gearshift sleeve as it approaches its final position.

Since the external collar 81) of the extension 8a ofthe driven shaft 8 is provided preferably with piston rings for the purpose of mutual alignment of the parts 8a, 15' and 32 and since these piston rings could be caught in an annular groove, such an annular groove instead of the axial grooves 37 should be provided in the gearshift sleeve 15 only when care is taken that the piston rings are eliminated.

If no rapid piston motions need be damped, then as a modification of the just described design the annular groove can be made substantially narrower, approximately as narrow as the axial grooves are long, or instead of an annular groove there can be provided just such axial grooves, in which instance the external collar I of the extension 8a of the driven shaft 8 can then likewise be provided with piston rings.

As was mentioned above, either an indicating mechanism or a signaling mechanism and/or a servomechanism can be connected to the alarm channel 35. Such an indicating mechanism is indicated at 39 in FIGS. 3 and 5. Let us first assume the instance that the alarm channel leads to an indicating mechanism 39 that provides a visual display on the control board, for example. If the gearshift sleeve 15 is in the engaged position, then the fluid pressure prevailing in the cylindrical volume A and holding the gearshift sleeve in this position provides via the axial grooves 37, branch channel 35b and alarm channel 35 a visual display concerning the final position assumed by the gearshift sleeve in the engaged configuration. If the gearshift sleeve 15 moves even just slightly out of the engaged final position, then this visual display vanishes instantaneously since then the axial grooves 37 are covered by the cylindrical outer face of the external collar 8b of the extension 8a of the driven shaft 8. lf the annular groove reaches the cylindrical volume B during the displacement of the gearshift sleeve 15 out of the engaged final position into the disengaged position, then the fluid pressure prevailing therein can not only enter into the branch channel 350 via the annular groove 38 but via this annular groove can also emerge out of the cylindrical volume B via the external collar 8c of the extension 8a of the driven shaft 8 so that the fluid pressure prevailing in this cylindrical volume is indeed sufficient to move the gearshift sleeve 15 out of the engaged position into the disengaged position but is not large enough to supply a visual display on the indicating mechanism 39 via the branch channel 35c and the alarm channel 35. This occurs only shortly before the gearshift sleeve 15 has reached its disengaged final position, since then, as is evident from the lower half of FIG. 3, the cylindrical inner face of the gearshift sleeve 15 still remaining beside the annular groove 38 comes into close overlap with the cylindrical external face of the external collar 8c and consequently the entire fluid pressure prevailing in the cylindrical volume B appears at the branch channel 35c and thus also at the alarm channel 35. Thus. in each instance the visual display mechanism 39 provides a visual indication that the gearshift sleeve 15 has assumed either its engaged final position or its disengaged final position, whereas this visual indication vanishes as long as the gearshift sleeve is between one or the other final position. If an acoustic signaling mechanism is connected to the alarm channel 35, then it can be so connected that a signal is emitted as long as the gearshift sleeve 15 assumes an intermediate position. whereas the signal emission ceases at the instant when the gearshift sleeve has reached one of its two final positions. Thus, if the previously described automatic disengagement of the gearshift sleeve 15 occurs due to a damage to the diesel engine 102, then this is also reported to the engine personnel either by a visual indication or by an acoustic signal.

A manually actuatable pressure-release valve 115 is preferably installed in the engagement channel 33 or in the line connecting to the latter, appropriately near the control device 111. Such a pressure release valve makes it possible for the engine personnel to instantly reduce the pressure prevailing in the cylindrical volume A upon recognizing an engine damage causing a con- Siderable drop in rotational speed or a halting of the diesel engine 102, and thus to cause an immediate disengagement of the gearshift sleeve 15 in the sense of an instant isolation of the diesel engine 102 from the propeller shaft 104, before the tractive torque of the ships propeller has caused an automatic disengagement of the gearshift sleeve 15 in the above-described manner.

We shall now consider the case that the alarm channel 35 or the line connected to it is connected to a servomechanism 112 indicated in FIG. and that this servomechanism acts on the pressure release valve 115 situated in the line of the engagement channel 33. It shall further be assumed that an engine damage causing a considerable drop in rotational speed or a halting of the diesel enginne 102 remains unnoticed by the engine personnel for some reason. If the above-described automatic disengagement of the gearshift sleeve now occurs under the action of the tractive torque of the ships propeller, then, since at the beginning of the disengagement motion the axial grooves 37 are covered by the cylindrical outer face of the external collar 81: of the extension 8a of the driven shaft 8, there occurs a brief pressure drop in the alarm channel 35 which is also communicated to the servomechanism 112. In turn, the servomechanism effects an immediate opening of the pressure-release valve 115 installed in the line of the engagement channel 33 so that now the disengagement of the gearshift sleeve 15 is effected in the very briefest time and the diesel engine 102 is instantly isolated from the ships propeller. In so doing, a signal can simultaneously be emitted in the engine room.

As a further development of such an arrangement, the servomechanism 112 can also be under the influence of one or more temperature monitors 116 which are installed in the diesel engine 102 and which monitor the temperature of the cylinder liner, for example, so that the servomechanism 112 is quickly actuated when abnormal operating conditions occur at the diesel engine 102. A remote-reading thermometer 117 can be connected to the temperature monitor or monitors 116.

As is also evident in FIG. 3, a pressure-fluid outlet opening 40 provided with a restrictor can be arranged in the alarm channel 35. The purpose of this throttle opening 40 is to cause the quickest possible pressure drop in the alarm channel 35 in the event that there is a halt in the pressure-fluid supply front one of the cylindrical volumes A or B to the alarm channel. It thus brings about an increase in the response sensitivity of the arrangement.

At least one of the confronting faces of the spurtoothed gear rings 14 and 17 can be provided in a known mannershown in FIG. 6 with deflection bevels which prevent an engagement of these gear rings as long as the driven shaft 8 overruns the drive shaft 1. If the cylindrical volume A is under fluid pressure and if the faces of the two gear rings 14 and 17 to be engaged in each other scrape over each other when the driven shaft 8 overruns, then the gearshift sleeve 15 thereby goes into axial oscillation whose frequency is determined by the pitch of the gear rings and by the relative rotation speed of the two gear rings. These oscillations are transmitted by the piston 15a to the pressure fluid situated in the cylindrical volume A and via the latter into all pressure-fluid channels and pressure-fluid lines leading into this cylindrical volume as well as into the devices connected thereto. It need not be mentioned that such oscillations are highly undesirable and under certain circumstances can lead to destruction. In order to be able to hold these oscillations in the cylindrical volume A, axial boreholes 41 are consequently arranged in the external collar 8b via which boreholes this cylindrical volume A is connected to small cylindrical volumes 43 arranged in an annular member 42 fastened to the extension 8a of the driven shaft 8, which smallcylindrical volumes are connected via openings 44 to a pressureless volume 45. In these small cylindrical volumes there are displaceable within limits small pistons 46 whose piston face is loaded via the borehole 41 by the pressure fluid situated in the cylindrical volume A and which small pistons are loaded by appropriately dimensioned pressure springs 47. Thus, if the gearshift sleeve 15 goes into axial oscillation due to scraping over each other of the facing beveled faces of the spur-toothed gear rings 14 and 17 when the driven shaft 8 overruns, then these oscillations transmitting themselves onto the pressure fluid situated in the cylindrical volume A are taken up by the small pistons 46 which go into corresponding oscillation. The pressurefluid oscillations are thereby localized to the cylindrical volume A and thus prevented from reaching into the channels and pressure-fluid lines connected to this cylindrical volume and to the devices connected thereto.

For the sake of improved clarity and simplicity of illustration, the individual actuation members 106, 107 108, 109, I l1, and are each indicated as separate actuation members in FIGS. 4 and 5. In practice, several of these actuation members are obviously combined in the usual manner into a single actuation member or are brought into mutual actuation dependence by means of suitable pressure means and/or constraining means.

In view of the above description, it is likely that modifications and improvements will occur to those skilled in the art which are within the scope of this invention.

What is claimed is:

l. A ships propulsion plant comprising:

a propulsion engine;

a drive shaft connected to said engine;

a propeller:

a driven shaft coupled to said propeller;

a variable-filling hydrodynamic coupling having an impeller and a turbine wheel, said impeller being rigidly connected to said drive shaft and said turbine wheel being rigidly connected to said driven shaft;

a selectively engageable mechanical coupling to bypass said hydrodynamic coupling to connect said drive shaft to said driven shaft; and

control means for setting the power of said engine.

for setting the filling of said hydrodynamic coupling and for shifting said by-pass coupling;

wherein said by-pass coupling comprises:

a one-way safety coupling element; and

means for directly transmitting propulsion torque of said engine to said propeller and for automatically disengaging said one-way safety coupling element when reverse torque between said engine and said propeller exceeds a predetermined limiting value.

2. The ships propulsion plant according to claim 1 wherein the limiting value of the reverse torque is in the range of the noload braking torque of said engine.

3. The ships propulsion plant according to claim 1 wherein:

said means for transmitting propulsion torque and for automatically disengaging said one-way safety coupling element comprises a coarse pitch screw thread; and

said one-way safety coupling element comprises an axially movable gearshift sleeve adapted to be coupled to one element of said hydrodynamic coupling by means of said coarse pitch screw thread;

said by-pass coupling further comprising a spurtoothed gear for connecting said gearshift sleeve to the other element of said hydrodynamic coupling, one of said elements of said hydrodynamic coupling being connected to said drive shaft and the other being rigidly connected to said driven shaft.

4. The ships propulsion plant according to claim 3 wherein said coarse pitch screw thread forces said gearshift sleeve into the engaged position when said control means is shifted to transmit the propulsion torque of said engine to said propeller, and said coarse pitch screw thread displaces said gearshift sleeve axially to a disengaged position under the influence of re erse torque of said predetermined value.

5. The ship's propulsion plant according to claim 4, said by-pass coupling further comprising torque limiting means coupled between said control device and said gearshift sleeve to prevent disengagement of said gearshift sleeve until the reverse torque has reached at least said predetermined value, said coarse pitch screw thread acting against said torque limiting means to axially displace said gearshift sleeve.

6. The ships propulsion plant according to claim 5 wherein:

said by-pass coupling is mechanically shiftable;

said torque limiting means comprises a spring link;

and

said control means for shifting said by-pass coupling comprises a mechanical linkage coupling said spring link to said gearshift sleeve.

7. The ships propulsion plant according to claim 5 wherein:

said by-pass coupling is mechanically shiftable;

said torque limiting means comprises a pressure limiting valve; and

said control means for shifting said by-pass coupling comprises a mechanical linkage coupling said pressure limiting valve to said gearshift sleeve.

8. The ships propulsion plant according to claim I wherein said by-pass coupling is accommodated inside the housing of said hydrodynamic coupling.

9. The ship's propulsion plant according to claim 3 wherein said gearshift sleeve and one of said shafts are formed with mating spur-toothed gear coupling elements, the confronting face of one of said spur-toothed gear coupling elements being formed with deflection bevels to prevent engagement of said by-pass coupling whenever the element of said hydrodynamic coupling connected to said propeller overruns the element of said hydrodynamic coupling connected to said engine.

10. A ships propulsion plant comprising:

a propulsion engine;

a drive shaft connected to said engine;

a propeller;

a driven shaft coupled to said propeller;

a variable-filling hydrodynamic coupling connected between said drive shaft and said driven shaft;

a selectively engageable mechanical coupling to bypass said hydrodynamic coupling to connect said drive shaft to said driven shaft;

control means for setting the power of said engine.

for setting the filling of said hydrodynamic coupling and for shifting said by-pass coupling;

wherein said by-pass coupling comprises:

a one-way safety coupling element;

means for transmitting propulsion torque of said engine to said propeller and for automatically disengaging said one-way safety coupling element when reverse torque between said engine and said propeller exceeds a predetermined limiting value, said means for transmitting propulsion torque and for automatically disengaging said one-way safety coupling element comprises a coarse pitch screw thread, said one-way safety coupling element comprises an axially movable gearshift sleeve being coupled to one element of said hydrodynamic coupling by means of said coarse pitch screw thread;

a spur-toothed gear for connecting said gearshift sleeve to the other element of said hydrodynamic coupling, one of said elements of said hydrodynamic coupling being connected to said drive shaft and the other being connected to said driven shaft; and

torque limiting means coupled between said control means and said gearshift sleeve to prevent disengagement of said gearshift sleeve until the reverse torque has reached at least said predetermined value, said coarse pitch screw thread acting against said torque limiting means to axially displace said gearshift sleeve, said coarse pitch screw thread forcing said gearshift sleeve into the engaged position when said control means is set to transmit the propulsion torque of said engine to said propeller, and, with the same setting of said control means said coarse pitch screw thread displacing said gearshift sleeve axially to a disengaged position under the influence of reverse torque exceeding said predetermined value; and

a pressure-fluid source;

wherein said torque-limiting means comprises a pressure limiting valve, said gearshift sleeve and one of said shafts are mutually constructed as a doubleacting piston and cylinder arrangement. said bypass coupling is hydraulically shiftable. and said control means for shifting said by-pass coupling comprises hydraulic transmission means coupling said pressure-fluid source and said pressure limiting valve to said piston and cylinder arrangement to thereby control relative axial motion between said piston and said cylinder.

11. The ships propulsion plant according to claim and further comprising axial stops for limiting the axial motion of said gearshift sleeve;

12. The ships propulsion plant according to claim 10 wherein said hydraulic transmission means comprises an engagement channel coupled between said control means and one side of said double-acting piston and cylinder arrangement, and a disengagement channel coupled between said control means and the other side of said double-acting piston and cylinder arrangement.

13. A ships propulsion plant comprising:

a propulsion engine;

a drive shaft connected to said engine;

a propeller;

a driven shaft coupled to said propeller;

a variable-filling hydrodynamic coupling connected between said drive shaft and said driven shaft;

a selectively engageable mechanical coupling to bypass said hydrodynamic coupling to connect said drive shaft to said driven shaft, said by-pass coupling being hydraulically shiftable; and

control means for setting the power of said engine,

for setting the filling of said hydrodynamic coupling and for shifting said by-pass coupling;

wherein said by-pass coupling comprises:

a one-way safety coupling element; and

means for transmitting propulsion torque of said engine to said propeller and for automatically disengaging said one-way safety coupling element when reverse torque between said engine and said propeller exceeds a predetermined limiting value, said one-way safety coupling element comprises a gearshift sleeve, said gearshift sleeve and one of said shafts being mutually constructed as a double-acting piston and cylinder arrangement, said gearshift sleeve being formed as the piston element and the cylinder element is formed as part of said shaft, said shaft is formed with engagement and disengagement channels for conducting pressure fluid to said piston and cylinder arrangement under control of said control means through respective pressure-fluid lines.

14. The ships propulsion plant according to claim 13 wherein:

said double-acting piston and cylinder arrangement includes a first cylinder volume and a second cylinder volume;

said shaft is formed with an alarm channel connected by a first radial branch channel to said first cylinder volume and by a second radial branch channel to said second cylinder volume: said propulsion plant further comprising: 5 an indicating mechanism; and

an alarm line connecting said alarm channel to said indicating mechanism; said gearshift sleeve is formed with surface grooves which are axially dimensioned and arranged that said first radial branch channel couples said first cylinder volume to said alarm channel only when said gearshift sleeve is in the fully engaged position and said second radial branch channel couples said second cylinder volume to said alarm channel when said gearshift sleeve is not in the fully engaged position. 15. The ships propulsion plant according to claim 14 wherein:

said indicating mechanism includes a servomecha- 20 nism;

said engagement pressure-fluid line includes a pres sure-release valve actuated by said servomechanism, said pressure release valve being opened by 5 said servomechanism when the fluid pressure in said alarm channel drops below a predetermined normal value. 16. The ships propulsion plant according to claim 15 wherein:

said pressure release valve is additionally openable by manual means; said propulsion plant further comprises a temperature monitor mounted to said engine and being coupled to said servomechanism for actuation thereof.

17. The ships propulsion plant according to claim 14 wherein:

said gearshift sleeve and one of said shafts are formed with mating spur-toothed gear coupling elements, the confronting face of one of said spur-toothed gear coupling elements being formed with deflection bevels to prevent engagement of said by-pass coupling whenever the element of said hydrodynamic coupling connected to said propeller overruns the element of said hydrodynamic coupling connected to said engine;

said propulsion plant further comprising at least one elastic reservoir connected to said first cylinder volume and capable of holding that amount of fluid displaced from said first cylinder volume by said axial oscillations.

18. The ships propulsion plant according to claim 17 wherein said elastic reservoir comprises a nonpressurized volume within said hydrodynamic coupling housing connected to said first cylinder volume by means of at least one borehole; and at least one spring loaded piston displaceable within said borehole.

l l l 

1. A ship''s propulsion plant comprising: a propulsion engine; a drive shaft connected to said engine; a propeller; a driven shaft coupled to said propeller; a variable-filling hydrodynamic coupling having an impeller and a turbine wheel, said impeller being rigidly connected to said drive shaft and said turbine wheel being rigidly connected to said driven shaft; a selectively engageable mechanical coupling to by-pass said hydrodynamic coupling to connect said drive shaft to said driven shaft; and control means for setting the power of said engine, for setting the filling of said hydrodynamic coupling and for shifting said by-pass coupling; wherein said by-pass coupling comprises: a one-way safety coupling element; and means for directly transmitting propulsion torque of said engine to said propeller and for automatically disengaging said one-way safety coupling element when reverse torque between said engine and said propeller exceeds a predetermined limiting value.
 1. A ship''s propulsion plant comprising: a propulsion engine; a drive shaft connected to said engine; a propeller; a driven shaft coupled to said propeller; a variable-filling hydrodynamic coupling having an impeller and a turbine wheel, said impeller being rigidly connected to said drive shaft and said turbine wheel being rigidly connected to said driven shaft; a selectively engageable mechanical coupling to by-pass said hydrodynamic coupling to connect said drive shaft to said driven shaft; and control means for setting the power of said engine, for setting the filling of said hydrodynamic coupling and for shifting said by-pass coupling; wherein said by-pass coupling comprises: a one-way safety coupling element; and means for directly transmitting propulsion torque of said engine to said propeller and for automatically disengaging said one-way safety coupling element when reverse torque between said engine and said propeller exceeds a predetermined limiting value.
 2. The ship''s propulsion plant according to claim 1 wherein the limiting value of the reverse torque is in the range of the no-load braking torque of said engine.
 3. The ship''s propulsion plant according to claim 1 wherein: said means for transmitting propulsion torque and for automatically disengaging said one-way safety coupling element comprises a coarse pitch screw thread; and said one-way safety coupling element comprises an axially movable gearshift sleeve adapted to be coupled to one element of said hydrodynamic coupling by means of said coarse pitch screw thread; said by-pass coupling further comprising a spur-toothed gear for connecting said gearshift sleeve to the other element of said hydrodynamic coupling, one of said elements of said hydrodynamic coupling being connected to said drive shaft and the other being rigidly connected to said driven shaft.
 4. The ship''s propulsion plant according to claim 3 wherein said coarse pitch screw thread forces said gearshift sleeve into the engaged position when said control means is shifted to transmit the propulsion torque of said engine to said propeller, and said coarse pitch screw thread displaces said gearshift sleeve axially to a disengaged position under the influence of reverse torque of said predetermined value.
 5. The ship''s propulsion plant according to claim 4, said by-pass coupling further comprising torque limiting means coupled between said control device and said gearshift sleeve to prevent disengagement of said gearshift sleeve until the reverse torque has reached at least said predetermined value, said coarse pitch screw thread acting against said torque limiting means to axially displace said gearshift sleeve.
 6. The ship''s propulsion plant according to claim 5 wherein: said by-pass coupling is mechanically shiftable; said torque limiting means comprises a spring link; and said control means for shifting said by-pass coupling comprises a mechanical linkage coupling said spring link to said gearshift sleeve.
 7. The ship''s propulsion plant according to claim 5 wherein: said by-pass coupling is mechanically shiftable; said torque limiting means comprises a pressure limiting valve; and said control means for shifting said by-pass coupling comprises a mechanical linkage coupling said pressure limiting valve to said gearshift sleeve.
 8. The ship''s propulsion plant according to claim 1 wherein said by-pass coupling is accommodated inside the housing of said hydrodynamic coupling.
 9. The ship''s propulsion plant according to claim 3 wherein said gearshift sleeve and one of said shafts are formed with mating spur-toothed gear coupling elements, the confronting face of one of said spur-toothed gear coupling elements being formed with deflection bevels to prevent engagement of said by-pass coupling whenever the element of said hydrodynamic coupling connected to said propeller overruns the element of said hydrodynamic coupling connected to said engine.
 10. A ship''s propulsion plant comprising: a propulsion engine; a drive shaft connected to said engine; a propeller; a driven shaft coupled to said propeller; a variable-filling hydrodynamic coupling connected between said drive shaft and said driven shaft; a selectively engageable mechanical coupling to by-pass said hydrodynamic coupling to connect said drive shaft to said driven shaft; control means for setting the power of said engine, for setting the filling of said hydrodynamic coupling and for shifting said by-pass coupling; wherein said by-pass coupling comprises: a one-way safety coupling element; means for transmitting propulsion torque of said enGine to said propeller and for automatically disengaging said one-way safety coupling element when reverse torque between said engine and said propeller exceeds a predetermined limiting value, said means for transmitting propulsion torque and for automatically disengaging said one-way safety coupling element comprises a coarse pitch screw thread, said one-way safety coupling element comprises an axially movable gearshift sleeve being coupled to one element of said hydrodynamic coupling by means of said coarse pitch screw thread; a spur-toothed gear for connecting said gearshift sleeve to the other element of said hydrodynamic coupling, one of said elements of said hydrodynamic coupling being connected to said drive shaft and the other being connected to said driven shaft; and torque limiting means coupled between said control means and said gearshift sleeve to prevent disengagement of said gearshift sleeve until the reverse torque has reached at least said predetermined value, said coarse pitch screw thread acting against said torque limiting means to axially displace said gearshift sleeve, said coarse pitch screw thread forcing said gearshift sleeve into the engaged position when said control means is set to transmit the propulsion torque of said engine to said propeller, and, with the same setting of said control means said coarse pitch screw thread displacing said gearshift sleeve axially to a disengaged position under the influence of reverse torque exceeding said predetermined value; and a pressure-fluid source; wherein said torque-limiting means comprises a pressure limiting valve, said gearshift sleeve and one of said shafts are mutually constructed as a double-acting piston and cylinder arrangement, said by-pass coupling is hydraulically shiftable, and said control means for shifting said by-pass coupling comprises hydraulic transmission means coupling said pressure-fluid source and said pressure limiting valve to said piston and cylinder arrangement to thereby control relative axial motion between said piston and said cylinder.
 11. The ship''s propulsion plant according to claim 10 and further comprising axial stops for limiting the axial motion of said gearshift sleeve.
 12. The ship''s propulsion plant according to claim 10 wherein said hydraulic transmission means comprises an engagement channel coupled between said control means and one side of said double-acting piston and cylinder arrangement, and a disengagement channel coupled between said control means and the other side of said double-acting piston and cylinder arrangement.
 13. A ship''s propulsion plant comprising: a propulsion engine; a drive shaft connected to said engine; a propeller; a driven shaft coupled to said propeller; a variable-filling hydrodynamic coupling connected between said drive shaft and said driven shaft; a selectively engageable mechanical coupling to by-pass said hydrodynamic coupling to connect said drive shaft to said driven shaft, said by-pass coupling being hydraulically shiftable; and control means for setting the power of said engine, for setting the filling of said hydrodynamic coupling and for shifting said by-pass coupling; wherein said by-pass coupling comprises: a one-way safety coupling element; and means for transmitting propulsion torque of said engine to said propeller and for automatically disengaging said one-way safety coupling element when reverse torque between said engine and said propeller exceeds a predetermined limiting value, said one-way safety coupling element comprises a gearshift sleeve, said gearshift sleeve and one of said shafts being mutually constructed as a double-acting piston and cylinder arrangement, said gearshift sleeve being formed as the piston element and the cylinder element is formed as part of said shaft, said shaft is formed with engagement and disengagement channels for conducting pressure fluid to said piston and cylinder arrangement under control of said control means through respective pressure-fluid lines.
 14. The ship''s propulsion plant according to claim 13 wherein: said double-acting piston and cylinder arrangement includes a first cylinder volume and a second cylinder volume; said shaft is formed with an alarm channel connected by a first radial branch channel to said first cylinder volume and by a second radial branch channel to said second cylinder volume; said propulsion plant further comprising: an indicating mechanism; and an alarm line connecting said alarm channel to said indicating mechanism; said gearshift sleeve is formed with surface grooves which are axially dimensioned and arranged that said first radial branch channel couples said first cylinder volume to said alarm channel only when said gearshift sleeve is in the fully engaged position and said second radial branch channel couples said second cylinder volume to said alarm channel when said gearshift sleeve is not in the fully engaged position.
 15. The ship''s propulsion plant according to claim 14 wherein: said indicating mechanism includes a servomechanism; said engagement pressure-fluid line includes a pressure-release valve actuated by said servomechanism, said pressure release valve being opened by said servomechanism when the fluid pressure in said alarm channel drops below a predetermined normal value.
 16. The ship''s propulsion plant according to claim 15 wherein: said pressure release valve is additionally openable by manual means; said propulsion plant further comprises a temperature monitor mounted to said engine and being coupled to said servomechanism for actuation thereof.
 17. The ship''s propulsion plant according to claim 14 wherein: said gearshift sleeve and one of said shafts are formed with mating spur-toothed gear coupling elements, the confronting face of one of said spur-toothed gear coupling elements being formed with deflection bevels to prevent engagement of said by-pass coupling whenever the element of said hydrodynamic coupling connected to said propeller overruns the element of said hydrodynamic coupling connected to said engine; said propulsion plant further comprising at least one elastic reservoir connected to said first cylinder volume and capable of holding that amount of fluid displaced from said first cylinder volume by said axial oscillations. 